What is creosote

A product of incomplete combustion: deposits of unburned, flammable tar vapors from wood smoke. Sometimes it is crusty or flaky in texture, but often sticky or hard. Creosote deposits are often hard to remove from chimneys, and pose a serious fire hazard.

One of the great misunderstandings in the world of wood-stoves is how creosote fits into the picture. Contrary to popular belief, creosote is not an inevitable product of wood burning. Creosote only forms when wood is burned incompletely, and is an indication of improper use, poor installation, or a poor wood stove design. It can and should be avoided.

It is also extremely flammable, and is responsible for many chimney-related structural house fires each year.

The long and the short of it…If you find a buildup of creosote in your stove pipe or chimney, have the chimney swept right away, and determine what’s causing it. There are four basic possibilities:

Operating your stove at a too-low burn rate

If you close the air flow to the stove down too low, for a long, low burn, you will create a smoky fire that emits lots of unburned tar vapours into the flue. Since the temperature of the flue gasses will already be relatively low, these vapours will be especially likely condensed inside the pipe or chimney flue.

The solution is to keep the fire burning at a moderately-active rate. Go outside and check the flue. If lots of smoke is billowing from the chimney, you are burning it too low. Yes, this means you can’t get as long a burn time from a load of wood, but you will actually get more heat from the same amount of wood, since creosote represents unburned fuel. You will also do your chimney and our environment a favour.

Using the wrong type of fuel

Burning green, wet, (or excessively dry wood this may spark) will cause creosote buildup. Burn only well seasoned, dry wood and untreated wood. Ideally wood should have a moisture content of less than 25%. On average it will take 12 months to dry out an inch depth of wood. Do not try and burn wood in an appliance that is designed to burn smokeless coal.

Oversized flue or improper connection

If the chimney isn’t quickly drawing the combustion products to the outdoors, due to an oversized flue, an excessively-long stove pipe, or too many elbows in the stove pipe – all of which tend to increase the amount of time the smoke stays in the venting system – then the smoke will tend to condense in the flue, forming creosote.

Whilst you do not need to connect your stove to a liner this is always advisable, the stove is normally designed to work on a 6 inch outlet, so connecting it to a 9 inch square brick chimney is always going to cause you a creosote problem.


Its not only chimney sweeps that advise against slumber burning but Devon & somerset Fire and Rescue Service state

The most common cause of chimney fires are:

• infrequent sweeping and cleaning

• burning unseasoned wood

• improper appliance sizing

• overnight burning or smouldering wood for long periods in wood stoves.

If you think this may be you or if you have not have your wood stove swept in the last 3 months, it’s time to book your ProSweep chimney sweep today, call 01626 832051 now.